The idea of spread spectrum was first used to combat intentional jamming and interception during War World II. Commercially, a great part of spread spectrum communication system operate in an unlicensed band with sufficient bandwidth to perform communication. A suitable band is Industrial Scientific Medicine (ISM) band at 2.4 GHz, which is globally available. This band provides 83.5 MHz of radio spectrum. It has been adopted by Bluetooth® Special Interest Group (SIG) and IEEE Std 802.15.1, the first part of Wireless Personal Area Network (WPAN) specifications. Being designed as a low cost cable replacement, it can provide a unified and convenient wireless interface for applications within the distance of personal area, e.g. 10 meters. In order to avoid data collision by ambient interference, frequency hopping (FH) technique is adopted.
FHSS is one of the prevailing spread spectrum schemes and involves rapidly changing the carrier frequency of the narrow band data signal. The ISM band, however, is an unlicensed shared band that is exposed to radiation from other systems operating concurrently. IEEE Std 802.11(b), the Wireless Local Area Network (WLAN) specifications and its higher-speed extension, is another wireless communication specification in this band. WLAN is targeted at high-speed data exchange in the local area network (LAN) environment. At the same time, garage door remote control and cordless telephone are in the same band. This brings upgrading down of the transmission rate, even paralysis of the communication system The co-existence situation has drawn so much attention that a task group, TG2, in IEEE 802.15 is formed to study the modeling of performance degradation and the possible solutions.
Adaptive frequency hopping (AFH) has been proposed to solve the co-existent problem. AFH removes the interfered channels from the hopping sequence and then hops to the clean channels. Since a signal of IEEE 802.11(b) spans 22 MHz of bandwidth, Bluetooth® devices will have to remove 22 channels, each having 1 MHZ, to fully avoid frequency overlap with 802.11(b) devices. One known problem of AFH is that Federal Communications Commission (FCC) has placed a restriction on the channel usage of FH systems in the 2.4 GHz band. A system must have at least 75 channels and the occupation time of each channel must not exceed 0.4 second within 30 seconds. It implies that at least 75 channels should be kept and used uniformly to achieve full-time usage. Removal of more than 4 channels occupied by an IEEE 802.11b device from the 79 hopping channels of Bluetooth® would become infeasible. This restriction applies to Bluetooth® type 1 and type 2 devices but not to type 3 devices due to their relatively lower transmission power. Moreover, when there are reserved time slots for priority information transmitted or received, it is not wise to apply the same rule on them.
Therefore, there exists a need for a method and an apparatus for implementing adaptive hopping without violating the restrictions and implementing it selectively, depending on whether the information type is prioritized.
In one aspect of the present invention, a method for determining a hopping sequence for selecting a channel from M channels divided into Np partitions to reduce probability of data collision from interference in a FHSS communication system is provided. One host apparatus in the FHSS communication system stores Q predetermined partition sequences and receives a first sequence of the M channels. The method includes the steps of (1) measuring Np data collision ratios respectively corresponding to Np partitions, responsive to a RF signal, the Np data collision ratios having value of R(i), i is from 1 through Np and denotes an ith partition; (2) selecting a partition sequence from Q partition sequences, the partition sequence having a smallest value of a selection function H(p), wherein the selection function is a summation of R(i)* relative frequency of occurrence of the ith partition in each of Q partition sequences, p being from 1 through Q and denoting pth partition sequence; (3) mapping the first sequence of M channels to the selected partition sequence to produce a second sequence of M channels; and (4) responsive to a control signal, selecting one of the first sequence and the second sequence as the hopping sequence.
In another aspect of the present invention, an apparatus for determining a hopping sequence for selecting a channel from M channels divided into Np partitions to reduce probability of data collision from interference in a FHSS communication system is provided. The host apparatus stores Q predetermined partition sequences and receives a first sequence of M channels. The apparatus includes a measurement circuit for measuring Np data collision ratios respectively corresponding to Np partitions, responsive to a RF signal, the Np data collision ratios has value of R(i), i being from 1 through Np and denotes an ith partition; a first selector for selecting a partition sequence from Q partition sequences, the partition sequence having a smallest value of a selection function H(p), wherein the selection function is a summation of R(i)* relative frequency of occurrence of the ith partition in each of Q partition sequences, p being from 1 through Q and denoting pth partition sequence; a mapping circuit for mapping the first sequence of M channels to the selected partition sequence to produce a second sequence of M channels; and a second selector, responsive to a control signal, for selecting one of the first sequence and the second sequence as the hopping sequence.